Atom Site x y z occ M [μB] Fe1 3g 0.25683 0 0.5 0.95333 1.9(1) Mn1 3g 0.25683 0 0.5 0.04667 1.9(1) Fe2 3f 0.59764 0 0 0.03535 2.3(1) Mn2 3f 0.59764 0 0 0.96465 2.3(1)

The crystal and magnetic structure of themagnetocaloric compound FeMnP0.5Si0.5

Delft Days onMagnetocalorics24 - 25 Oct 2011

V. Höglina, M. Hudlb, M. Sahlberga, P. Nordbladb, P. Beranc, Y. Anderssona

a Department of Materials Chemistry, Uppsala University, Box 538, 75121 Uppsala, Swedenb Department of Engineering Science, Uppsala University, Box 516, 75120 Uppsala, Sweden

c Nuclear Physics Institute, Academy of Sciences of the Chech Republic, 25068 Rez, Czech Republic

- Samples of stoichiometric FeMnP0.5Si0.5 have been synthesized by the drop syn-thesis method with losses <0.5%.

- FeMnP0.5Si0.5 was con�rmed to cristallize in the hexagonal Fe2P-structure with the unit cell parameters a = 6.2090(3) Å and c = 3.2880(3) Å.

- The Fe atoms are mainly situated in the pyramidal 3g site while the tetragonal 3f site is prefered by the Mn atoms.

- The magnetic moments derived from neutron powder di�raction are shown to be coordinated along the a-axis with a total moment of 4.4 μB.

Conclusions

Experiments

ResultsPhase analysis Structure re�nements

Fig. 6: Experimental setup for the drop synthesis method using an induction furnace

Fig. 3: XRD-patterns of FeMnP0.5Si0.5 showing the structural transition occurring at approx. 385 K.

Fig. 2: X-ray powder di�raction pattern of FeMnP0.5Si0.5 at 296 K. The tick marks indicate the Bragg positions of FeMnP0.5Si0.5.

The XRD investigation con�rms that

FeMnP0.5Si0.5 crystallizes in the hexago-

nal Fe2P-type structure, space group

P-62m and unit cell parameters

a=6.2090(3) Å, c=3.2880(3) Å. The XRD

pattern for FeMnP0.5Si0.5 at 296 K is

shown in Fig. 2 which reveals a pattern

of a single phase sample. XRD-

patterns in the range 363–403 K are

shown in Fig. 3 where it can be seen

that FeMnP0.5Si0.5 undergoes an iso-

structural transition between 373 and

393 K. The a-axis has decreased 2%

while the c-axis has increased 5%

compared to 296 K.

The structural transition occurs in the

same region as the Curie temperature

why it is likely that the transition origi-

nate from magnetostriction e�ects.

Structure re�nements of neutron

powder di�raction data of FeMnP0.5Si0.5

at 296 K and 450 K can be seen in Fig. 4.

The data from the re�nements are sum-

marized in Table 1 and it can be seen

that the tetragonal 3g site is mainly oc-

cupied by the Fe atoms and has a mag-

netic moment of 1.9 μB. The Mn atoms

are mainly situated in the pyramidal 3f

site and has a magnetic moment of 2.5

μB. The total magnetic moment per unit

cell is thus approx 4.4 μB.

This high value of the magnetic

moment is con�rmed by Mössbauer re-

sults [2]. The magnetic structures of

FeMnP0.5Si0.5 and Fe2P are shown in Fig.

5. The magnetic moments are aligned

in the a-direction while the moments of

Fe2P are aligned in the c-direction [3].

The composition based on the re�ned

occupancies extracted from the neu-

tron powder di�raction data (at �xed

ratio P/Si=1) indicates that the acquired

composition of the metallic atoms in

the sample is close to FeMnP0.5Si0.5

(Fe1.02(1)Mn0.98(1)P0.5Si0.5, namely).

Sample preparationSamples of stoichiometric FeMnP0.5Si0.5 were

prepared by the drop synthesis method

using a high frequency induction furnace,

see Fig. 6. Raw materials were high purity

pieces of iron, manganese. phosphorous

and silicon. All samples were crushed,

pressed into pellets and sealed in evacuated

fused silica tubes. Subsequent, the samples

were sintered at 1373 K for 1 h, annealed at

1073 K for 65 h and �nally quenched in cold

water. The synthetic process showed minor

(less than 0.5 weight%) losses.

IntroductionRoom temperature magnetic refrigeration,

based on the magnetocaloric e�ect (MCE)

has attracted attention due to its energy

saving potentials and being friendly to the

environment because of the magnetic re-

frigeration cycle, see Fig. 1. The com-

pound FeMnP0.5Si0.5, based on the Fe2P-

system, has showed promising magneto-

caloric properties and due to its rather

cheap and non toxic elements it is pro-

posed that these type of compounds may

be a future for magnetic refrigeration.

ab

c

Fe (3g)

Mn (3f)

P/Si (2d)P/Si (1a)

ab

c

Fe (3g)

Fe (3f)

P (2d)

P (1a)

a)

b)

Fig. 5: The magnetic structure of FeMnP0.5Si0.5 (a) and Fe2P (b). The magnetic moments in Fe2P are aligned in the c-direction while the moments in FeMnP0.5Si0.5 are aligned in the a-direction. The length of the arrows corresponds to the magnitude of the magnetic mo-ments.

Fig. 4: Structure re�nements from neutron powder di�raction data of FeMnP0.5Si0.5 at 296 and 450 K. The peaks with the high-est magnetic intensity are marked with an arrow.

Contactviktor.hoglin@mkem.uu.se

References[1] V. Höglin, M. Hudl, M. Sahlberg, P. Nordblad, P. Beran, Y Andersson. J. Solid State Chem. 184 (2011), p. 2434[2] M. Hudl, L. Häggström, E-K. Delczeg-Czirjak, V. Höglin, M. Sahlberg, L Vitos, O. Eriksson, P. Nordblad, Y. Andersson. Appl. Phys. Lett. 99 (2011) p.152502.[3] L. Lundgren, G. Tarmohamed, O. Beckman, B. Carlsson and S. Rundqvist. Phys. Scr. 17 (1978), p. 39

Structure analysisPhase analysis and structure characterizations

were performed using X-ray and neutron powder

di�raction in the temperature range of 296 - 450 K.

Neutron powder di�raction data were collected

on the instrument MEREDIT at the Nuclear Physics

Institute in Rez, Czech Republic.

Structure re�nements were performed on the

neutron powder pro�les by the Rietveld method

using the software FULLPROOF and unit cell pa-

rameters from XRD data were re�ned using the

software UNITCELL

Atom Site x y z occ M [μB] Fe1 3g 0.25683 0 0.5 0.95333 1.9(1) Mn1 3g 0.25683 0 0.5 0.04667 1.9(1) Fe2 3f 0.59764 0 0 0.03535 2.5(1) Mn2 3f 0.59764 0 0 0.96465 2.5(1)

Table 1: Placement and occupancy of the Fe and Mn atoms in FeMnP0.5Si0.5 at 296 and 450 K. Derived from re�nements of neutron powder di�raction data.

This work is funded by

Fig. 1: Scheme of the magnetocaloric cycle.